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  3. Many of the world’s big lakes are threatened by pollution or huge drainage schemes. But there is least one fairly bright spot. T

Many of the world’s big lakes are threatened by pollution or huge drainage schemes. But there is least one fairly bright spot. T

admin2009-04-27  51
问题     Many of the world’s big lakes are threatened by pollution or huge drainage schemes. But there is least one fairly bright spot. The Great Lakes and St. Lawrence River system between Canada and the United States, which together account for a fifth of the world’s non-polar fresh water, are much healthier than they were. Can they stay that way?
    Though Lake Michigan is wholly the United States, all five lakes are governed by the Boundary Waters Treaty of 1909, implemented by an independent bi-national joint commission. In 1978, both countries agreed to try to clean up the water in the lakes, several of which were heavily polluted. They have done so though in fact the improvement owes as much to economic change as to government action. Steel and other heavy industry have given way to cleaner industries and services, both in Ontario and in American lakeside states. The result: tests on fish and birds show residues of heavy metals have declined (though dangerous levels of mercury are still found), while in past ten years the rivers near Toronto have been successfully stocked with salmon.
    There are still worries. One problem is farming. This uses much lake water 929% of the total that is withdrawn) from irrigation, while also polluting the lakes and river systems. The huge quantities of manure spread on farms in Ontario and Quebec also causes pollution, by running off the land into streams, rivers and then lakes.
    Some scientists also worry that water levels will fall permanently. Climate change is likely to cut rainfall in the Great Lakes basin, while ever more water will be drawn from the lakes by a rising urban population. General consumption in the basin will increase by 25% in the next 25 years, according to a forecast by a consultant to the commission.
    Other threats include some 140 exotic species of flora, fish and shellfish that have found their way into the lakes, some via ships’ ballast. The zebra mussel from Eastern Europe is the most notorious and probably most damaging to the environment. It consumes a lot of oxygen (though it also helps to clean the water). Lastly, there is the hazardous prospect of decommissioning Ontario’s two dozen ageing nuclear reactors, which line the shores of Lake Ontario and Lake Huron.
    Fortunately, the long history of successful cooperation between the two countries and among the local governments suggest these threats can be managed. Both governments have approved the commission’s plan to set up international watershed boards across the continent. These are to take a "holistic" approach to ecosystems. Maybe the Zebra mussel and the farm run-offs have met their match.
选项 A、are equally located between Canada and the U.S.
B、contain a small part of the world’s fresh water.
C、are governed neither by Canada nor by the U.S.
D、enjoy fresher water now than 25 years ago.
答案D
解析 题干的要求是，从文章中我们可以知道关于五大湖的什么?从第一段我们知道"加拿大和美国之间的五大湖和圣劳伦斯河一起占非极地淡水的五分之一，而且现在水质要好于以往"。接着在第二段又指出，尽管"整个密歇根湖在美国境内"，但两国在1978年同意共同清理该水域。因此我们可以得出正确答案。
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